A laser generates optical radiation (light) within a laser resonator (often referred to as a laser cavity). The optical radiation builds up within the laser resonator and eventually passes through a final optical surface (often referred to as the output coupler) of the resonator to propagate in space beyond the laser. Powerful lasers may be used for cutting, drilling, welding, marking, or engraving of materials. In particular, radio frequency (RF)-excited gas lasers produce laser energy when a gas medium within the laser is excited by the application of RF energy between a pair of electrodes. An example of a gas laser is a carbon dioxide (CO2) laser.
The performance parameters of a laser, particularly RF-excited gas lasers, may generally be characterized by the laser power, power stability, and beam mode quality. Each of these performance parameters may be affected by one or more conditions within the laser itself. For instance, changing conditions of the gas within the electrodes of an RF-excited gas laser may affect the uniformity of the gas discharge within the electrodes. This then affects the M2 (pronounced “M-squared”) parameter, which is defined as the ratio of a beam parameter product (BPP) of an actual beam to that of an ideal Gaussian beam at the same wavelength (e.g., a “beam quality factor”). Changing conditions of the gas within the electrodes also may affect other laser beam features such as ellipticity and/or roundness. In pulsed gas lasers, particularly where unstable resonators are used, acoustic resonances within the laser structure can lead to these changing conditions within the electrodes and hence, to poor beam quality and/or poor power stability. Thus, the laser's ability to effectively perform its intended purpose often may be degraded.